This invention relates to a diagnostic test device for fecal occult blood utilizing guaiac as the test indicator. More particularly, this invention relates to a test matrix such as paper impregnated with guaiac together with a combination of substances which according to the invention prevent false-positive results in the presence of peroxidases.
A sensitive, specific and simple laboratory test for colorectal cancer is helpful in screening patients for early neoplastic lesions.
A test already available is the Hemoccult slide test for occult blood in stool (see U.S. Pat. No. 3,996,006). This simple, inexpensive laboratory test is capable of detecting blood in stool that may be related to an early cancerous lesion of the gastrointestinal tract. The test rationale which uses guaiacimpregnated paper as a test matrix is based on the phenolic oxidation of guaiac by hemoglobin in the presence of hydrogen peroxide. The production of a blue color on the test paper usually indicates the presence of blood. However, there is a 4 to 6% false positive reaction (i.e., positive test reaction without disease) as a result of non-hemoglobin interfering compounds present in the stool. It has been found that these interfering compounds are peroxidases ubiquitous to bacterial flora in the gut and in certain food sources. Each false-positive test may result in an exhaustive clinical investigation that is costly to the patient and time consuming for the physician. Aside the waste of money and manpower, the patient may be subjected to tremendous anxiety as the presence of blood in the feces may be an indication of cancer or other serious maladies.
In order to reduce the incident of interference by peroxidase in the guaiac test procedure for hemoglobin, it is a usual practice to prohibit a patient from eating vegetable products that contain peroxidase, e.g., potato, cabbage, onions, horseradish, etc. for several days. This gives time for possible interfering substances to be cleared from the body. However, indigenously present perioxidase (bacterial peroxidase) may still interfere with the test. Also patients may inadvertantly or otherwise ingest interfering substance containing vegetables notwithstanding instructions to avoid them.
The reaction of hemoglobin in fetal occult blood with guaiac in the presence of hydrogen peroxide, to give a blue color, is a known method for detection of the presence of blood as discussed above. This reaction takes advantage of the peroxidase activity of hemoglobin, which is similar to the reaction of peroxidase enzymes except that the peroxidase enzyme reaction is due to biochemical enzymatic activity while hemoglobin is not an enzyme. It is the recognition that peroxidase reacts with guaiac through enzymatic action while hemoglobin does not, that forms the basis of the present invention. By at least partially denaturing the protein that forms the peroxidase enzyme and removing the calcium and magnesium ions necessary for efficient peroxidase enzyme activity from the reaction mixture, one can eliminate the interfering effect of the peroxidase without practically affecting the hemoglobin.
It is therefor an object to avoid the problems inherent in prior art techniques by deactivating interfering peroxidase that may be present.